1. Field of Invention
The present invention relates to a method of mechanically treating needle blanks used for fabrication into surgical needles, and more particularly to a method for deburring and chamfering said needle blanks.
2. Background of the Art
For many years, surgeons have employed needle-suture combinations in which a suture or ligature is attached to the shank end of a needle. Such needle-suture combinations are provided for a wide variety of monofilament and braided suture materials, both absorbable and nonabsorbable, e.g., catgut, silk, nylon, polyester, polypropylene, linen, cotton, and absorbable synthetic materials such as polymers and copolymers of glycolic and lactic acids.
Needle-suture combinations fall into two general classes: standard needle attachment and removable or detachable needle attachment. In the case of standard needle attachment, the suture is securely attached to the needle and is not intended to be separable therefrom, except by cutting or severing the suture. Removable needle attachment, by contrast, is such that the needle is separable from the suture in response to a force exerted by the surgeon. Minimum acceptable forces required to separate a needle from a suture (for various suture sizes) are set forth in the United States Pharmacopoeia (USP). The United States Pharmacopoeia prescribes minimum individual pull-out forces as measured for five needle-suture combinations. The minimum pull-out forces for both standard and removable needle-suture attachment set forth in the United States Pharmacopoeia are hereby incorporated by reference.
On typical method for securing a suture to a needle involves providing a cylindrical recess in the shank end of a needle and securing a suture therein. For example, U.S. Pat. No. 1,558,037 teaches the addition of a cement material to such a substantially cylindrical recess to secure the suture therein. Additional methods for bonding a suture within a needle bore are described in U.S. Pat. Nos. 2,928,395 (adhesives) and 3,394,704 (bonding agents). Alternatively, a suture may be secured within an axial bore in a needle by swaging the needle in the region of the recess. See, e.g., U.S. Pat. No. 1,250,114. Additional prior art methods for securing a suture within a needle bore include expansion of a catgut suture through the application of heat (U.S. Pat. No. 1,665,216), inclusion of protruding teeth within the axial bore to grasp an inserted suture (U.S. Pat. No. 1,678,361) and knotting the end of the suture to be inserted within the bore to secure the suture therein (U.S. Pat. No. 1,757,129).
Methods for detachably securing a suture to a needle are also well known. For example, U.S. Pat. Nos. 3,890,975 and 3,980,177 teach swaging a suture within a needle bore such that the suture has a pull-out value of 3 to 26 ounces. Alternative detachable attachment methods include providing a weakened suture segment (U.S. Pat. No. 3,949,756), lubricant tipping the end of a suture to be inserted in the axial bore of a needle (U.S. Pat. No. 3,963,031) and pretensioning a suture that is swaged within an axial needle bore (U.S. Pat. No. 3,875,946). See also, U.S. Pat. Nos. 3,799,169; 3,880,167; 3,924,630; 3,926,194; 3,943,933; 3,981,307; 4,124,027; and 4,127,133.
To fabricate a surgical needle, needle blanks are cut by conventional cutting means from wire stock. For those needle-suture combinations wherein the suture is inserted into a longitudinal cylindrical recess in the barrel end of the needle, one end of the needle blank is drilled by mechanical or laser means.
The cutting and drilling produces burrs, and, in the case of laser drilling, burn spots which must be removed. Also, the cutting process leaves a sharp, circumferential periphery at the butt end. If the sharp edge is not removed there is a possibility that a suture connected to the needle might be cut or damaged by coming into contact with the edge. This can occur, for example, if the suture is bent sharply around in the vicinity of the needle end.
Needle blanks, therefore, are subjected to mechanical treating to deburr and chamfer the needle blank.
Deburring and chamfering can be accomplished by any one of several machining techniques such as grinding, lathing, and tumbling.
Tumbling is a preferred method for deburring and chamfering because of its convenience. The needle blanks are placed in a drum with abrasive particles, e.g. and agitated by rotation of the drum. However, these abrasive particles, e.g., aluminum oxide, silicon oxide, zinc oxide, dull the surface. The abrasion, while deburring and chamfering the needle blank, also scratches the needle surface, thereby requiring a subsequent polishing step to renew the fine finish of the needle. Elimination of the extra polishing step would reduce the time and cost required to make a surgical needle.